Calloplax janeirensis (Gray, 1828)

Reyes-Gomez, Adriana, Ortigosa, Deneb & Simoes, Nuno, 2017, Chitons (Mollusca, Polyplacophora) from Alacranes Reef, Yucatan, Mexico, ZooKeys 665, pp. 1-36 : 1

Calloplax janeirensis (Gray, 1828) Figures 2 N–O, 5 A–H

Material examined.

Four specimens; 9-15.2 mm long, 4.9-7.1 mm wide. Isla Perez (CNMO4981, CNMO4990, CNMO4994).

Description.

Medium-sized chitons with elongate body shape. Color yellow, creamy, or light brown (Figure 2 N–O). Tegmentum strongly sculptured with large, raised coalesced pustules. Head valve (Figure 5A), semi-circular, with large lobulose pustules, arranged in 8-10 radiating, bifurcated rows, uplifted notch. Tail valve (Figure 5B), wider than long; mucro postmedian, not elevated and pointed; antemucronal area with 17-19 longitudinal, pustulose ribs, the pustules on the jugal area are less coalesced and arranged longitudinally; postmucronal area with 8-9 coarsely pustulose radial ribs. Intermediate valves (Figure 5C), semi-rectangular shaped, posterior margin almost straight; lateral areas heavily elevated with 2-3 coarsely pustulose bifurcate ribs; the rib adjacent to central area usually raised more than those near the posterior margin; central areas narrower than combined lateral areas, wider near its center; pleural areas with 7-8 longitudinal ribs, which can develop sub-riblets; 5-7 pustulose ribs in jugal areas, which fade toward the apex. White to slightly blue articulamentum; apophyses and insertion plates short and wide (Figure 5D); slit formula 7 –9/1/8– 10. Pustules bear large megalaesthetes and between them, the micraesthetes appear somewhat scattered (Figure 5E). Girdle colored in alternating irregular bands of green, cream and yellow; covered with small and medium strong ribbed scales, and hyaline long needles (Figure 5F), the scales are somewhat wider than longer, its apical end develop a flattened pit (Figure 5G), and between the scales occur single curve spicules, scattered with no apparent order. Radula (Figure 5H) with major lateral tooth tridentate, with broad and wide cusps; central tooth spatulate in shape, its distal end bending outwards and longer than minor lateral teeth.

Habitat.

Found in intertidal, on rock buried in sand, associated with crustose coralline red algae.

Remarks.

When Thiele (1909) described the genus Calloplax based on only its type species, Chiton janeirensis Gray 1828, he emphasized differences of its tegmental nodulose ribs contrasted with those of the distinct pustules for selected members of Chaetopleura Shuttleworth, 1853, where Pilsbry (1892) had previously assigned this species. Smith and Ferreira (1977), Ferreira (1978b) and Ferreira (1982) expanded Thiele’s genus to include three other species, with Ferreira (1978b) transferring it from Chaetopleuridae to Callistochitonidae , and then later (1982) transferring it back. Ferreira (1978b) designated and figured a lectotype from among the syntypes of Chiton janeirensis from the type locality of Rio de Janeiro, Brazil. Lyons (1985) questioned the reassignment of family status for Calloplax janeirensis , emphasizing the morphological similarities between Calloplax and Chaetopleura genera, also noted by Ferreira (1978b; 1982). Lyons (1985) acknowledged the uncertainty regarding both genera, and based on similar girdle elements and the continuity in the range of tegmental sculpturing in species assigned to Chaetopleura or Calloplax , he suggested that Calloplax should be considered a synonym of Chaetopleura s.s. This was later followed by Bullock et al. (1994) and Lyons and Moretzsohn (2009), but Van Belle (1983), Kaas and Van Belle (1994; 1998) and Sirenko (2006) recognized it as a separate genus and have followed Ferreira (1978b) in placing it in a subfamily or family, respectively, associated with Callistochiton , not Chaetopleura , based on the presence of heavily sculptured ribs, and the insertion plate slits that generally correspond in number and position to the dorsal radial ribs, which, according to these authors is not a state of character of Chaetopleurinae. Recognizing that its status remains controversial, here we have preferred to follow Sirenko (2006) for the assignment of Calloplax as a distinct genus within Callistochitonidae .

PNAA specimens (up to 15.2 mm), bear resemblance on sculpturing and number of ribs (I: 8 ribs; IV 2-3 ribs; VIII 9 ribs) to a 10.5 mm specimen of C. janeirensis described by Lyons (1985: figs 22-24) from Dry Tortugas, Florida Keys, for which he figured valves I (11 ribs), IV (2 ribs) and VIII (8 ribs). PNAA specimens show ribs that tend to merge and bifurcate, and the lateral areas seem to develop three pustulose ribs, which became two, after both ribs next to diagonal ridge merged into one. On the contrary, Florida Keys specimens show more rounded pustules, the ribs remain separate or well-defined, and the lateral areas display two separated ribs. The number of ribs on the pleural areas (8 ribs), antemucronal area (18 ribs) and postmucronal areas of tail valve (8 ribs), are similar in both species. Such differences between Florida Keys and PNAA can be explained by the chiton’s size. We assume that Lyons (1985) described a juvenile specimen. Examination of the lectotype (NHMUK 1977041/2) from Rio de Janeiro (16.2 mm) (Figure 14C), showed rounded pustules aligned in ribs, 12 on head valve, 3-4 on lateral areas, and 15 ribs on postmucronal area of tail valve. When comparing with the PNAA specimen (15.2 mm), the lectotype has no fusion between pustules and it has a higher number of ribs on the head valve, lateral and postmucronal areas. The pustule morphology and number of ribs, of the lectotype is similar to specimens that García-Ríos (2003: fig. 77-81) figured from Puerto Rico. Overall, the PNAA specimens showed similarities with previously figured specimens from the Bahamas, Florida and Puerto Rico in the girdle scales and spicules, and in the morphology of the major lateral radula teeth ( Ferreira 1978b, Lyons 1985, Kaas and Van Belle 1994, García-Ríos 2003).